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Left: Adult mouse brain section (45 μM; fixed by transcardial perfusion with 4% paraformaldehyde) across motor cortex was co-stained with RPCA-Calretinin (red) and our mouse monoclonal antibody to Fox3/NeuN (MCA-1B7; green). Middle: Adult mouse brain section across visual cortex was co-stained with RPCA-Calretinin (red) and our chicken polyclonal antibody to calbindin (CPCA-Calb; green). Calretinin and calbindin label different population of neurons in the brain. As a result, most cells were labeled with one of the two antibodies and appear to be either red or green. However in visual cortex, a few cells express both proteins and appear to be yellow. Right: Adult rat brain section (45 μM; fixed by transcardial perfusion with 4% paraformaldehyde) across hippocampal CA1 region was co-stained with RPCA-Calretinin (red) and our mouse monoclonal antibody to parvalbumin (MCA-3C9; green). The two antibodies stain distinct subsets of interneurons in the pyramidal layer and the positively labeled cells appear to be either red or green. Insets show high magnification pictures of boxed are in each image. Blue is a Hoechst staining that labels DNA.

Left: Blot of 20μg of rat brain lysates probed with RPCA-Calretinin at 1:5,000. The antibody recognizes a clear band at ~29 kDa as expected. Right: At the same antibody concentration we probed a blot on which were 0.2μg of recombinant human parvalbumin (lane 1), recombinant human calretinin (lane 2) and recombinant human calbindin (lane 3). RPCA-Calretinin reacts only with the calretinin protein, and not the two related proteins parvalbumin and calbindin.

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Calretinin, first described in 1987, acquired its name based on homology with calcium binding protein calbindin and the tissue of first detection, the chick retina (1). As a member of the large superfamily of cytoplasmic Ca2+ binding proteins, calretinin belongs to the subclass of these containing the “EF hand” Ca2+ binding motif originally characterized in parvalbumin (2). Calretinin is expressed in mammalian central nerve system, testis, fallopian tube and pancreas. In the brain it is localized in certain classes of neurons, and antibodies to it are useful for identifying specific neuronal cell types (3). It is particularly concentrated in some cerebellar granular cells and their parallel fibers, but is also found in many GABAergic interneurons in the cortex. These GABAergic interneurons, in most cases, express only one of three Ca2+ binding proteins, namely calretinin, calbindin or parvalbumin . As a result, these important inhibitory interneurons can be identified and subclassified based on their expression of one or other of these proteins (3). Each type of neuron as defined in this fashion has particular electrophysiological and functional properties. For example, calbindin positive interneurons are not fast-spiking as are parvalbumin expressing interneurons. Human calretinin is also known as 29 kDa calbindin and calbindin-2, for its sequence is related to calbindin.

Calretinin contains six EF-hand domains. Four of them bind Ca2+ with high affinity in a cooperative manner, one with low affinity and the last one is non-functional, without Ca2+-binding ability (4,5). The function of calretinin appears to be primarily buffering the Ca2+ level in cells and affect intracellular calcium signals. Calretinin deficiency in mossy cells of the dentate gyrus and granule cells results in abnormal excitability in the cerebellar neuronal network and impairment of long-term potentiation and motor coordination (6). The HGNC name for this protein is CALB2.

This antibody was raised against human calretinin protein expressed in and purified from E.coli. This antibody does not cross-react with the related calcium binding proteins calbindin and parvalbumin (see Blot image).

Our company's goal is to be the leader in the development and commercialization of unique, well-characterized antibody reagents and ELISA type assays for academic and biopharmaceutical research. If we say that an antibody will work in a particular assay, rest assured that it will. Since we make the vast majority of our antibodies in house we are also able to offer very competitive pricing!